Here's why a lone single victory is important, even in a caucus:
If there are a lot of voters who like RP but believe he can't winning, well winning a state, even a small one like Maine, ends that argument.
If there are a lot of voters who think RP is "crazy", winning ends that argument. Because crazy people don't win whole states.
So by winning in Maine, beating Romney again, not only damages his brand it improves ours tremendously because it gets rid of two arguments that holds back a lot of non-aligned voters. You can't call us fringe if we win a state. Our legitimacy soars if this happens. That's what at stake in Maine.